Catheter delivery systems are commonly used to introduce self-expanding endoprostheses in human or animal bodies and to advance them to the clogged or narrowed area. In the delivery system, the elongate endoprosthesis is held in a radially compressed state by a surrounding sheath to facilitate a smooth delivery. When the endoprosthesis has been placed in the destined area, it is expanded by withdrawing or opening up the sheath.
A catheter delivery system where the endoprosthesis is expanded by cutting open the sheath is disclosed in FR 2688688. In this system, three cutting wires are arranged equidistantly around the periphery of the endoprosthesis. Each wire runs from a proximal end of the catheter to a distal end, with the wire placed between the radially compressed endoprosthesis and the sheath in the region where the endoprosthesis is received, leaves the sheath at its distal end and runs back to the proximal catheter end along the outside of the sheath, so as to form a loop around the sheath wall. Both parts of the wires, in- and outside the sheath, are guided parallel to one another and the overall six proximal wire ends are attached to a handle at the proximal end of the catheter. The sheath is opened by pulling the handle so that the distal ends of the three wire loops move proximally and cut through the wall of the sheath. The disclosure of U.S. Pat. No. 5,755,769 is similar.
A catheter delivery system that uses only one cutting wire is disclosed in WO-A-01/08599 of Angiomed GmbH & Co. Medizintechnik KG. The wire consists of an inner pull element, running within the sheath, an outer pull element, running outside the sheath, and a separating element, located between the distal ends of the two pull elements at the distal end of the sheath. In order to expand the endoprosthesis, both pull elements are simultaneously pulled in a proximal direction, so that the separating element moves along the endoprosthesis towards the proximal catheter end and cuts through the sheath wall. The disclosure of EP-A-732087 is similar, and expresses a preference for polyethylene-terephthalate as material for the body of the sheath because it tears easily after being notched. The disclosed system is a balloon catheter with a collar from which the sheath extends distally and a strand extends proximally. Pulling on the strand pulls the split sheath proximally away from the stent.
In known catheter delivery systems that use a cutting mechanism to open up the sheath, the cut open sheath is trapped between the expanded endoprosthesis and the wall of the vessel, once the expansion process is finished. To remove the sheath from the patient's body, it has to be pulled out from its proximal end. For the case of relatively large endoprostheses, such as oesophagus stents, where sheaths with thick walls can be used, this procedure is normally uncomplicated. However, problems arise when small-sized endoprostheses are required, for example to widen narrow blood vessels. In this case, the profile of the distal catheter end, comprising the endoprosthesis to be deployed, has to be strongly reduced, in order to facilitate accurate placement of the endoprosthesis and thus sheaths with thin walls have to be used. When such a thin-walled, cut open sheath is removed from the patient's body by pulling from its proximal end, the friction generated by the abluminal surface of the expanded endoprosthesis and the luminal surface of the vessel may cause either the sheath to tear, inhibiting its complete removal, or the endoprosthesis to move proximally with the sheath being pulled away from the axial position in the bodily lumen where it ought to be. Similar friction problems may arise even in traditional deployment methods, where an unslitted sheath is withdrawn from the endoprosthesis in the expansion process. When pulled from the proximal end, a thin-walled sheath may stretch along the direction of the pull, leading to a decrease of its radial diameter. This increases the friction caused between sheath and endoprosthesis, requiring a larger pulling force to move the sheath, similar to the known concept of the “Chinese finger trap”. Eventually, the sheath may tear or the endoprosthesis may move away from the desired position.
Also belonging to the state of the art is WO2004/066809, Gore, which suggests to use a deployment line that is integral with a pull back sheath, to release an endoluminal device from inside the sheath.
WO98/20812 Cook, Inc. discloses a splittable sleeve stent deployment device in several embodiments, in one of which an enlarged diameter distal shaft portion is withdrawn proximally through the lumen of the stent to burst a sleeve surrounding the stent. In another embodiment, the sleeve continues distally into a partial sleeve segment that is folded back inside the sleeve to end in a graspable proximal end proximal of the stent. Pulling proximally on this end can have the effect of splitting the sleeve to release the stent. The sleeve can be made from molecular oriented PTFE.
US2006/0089627 is another disclosure of a stent within a sleeve that is parted by a device that moves proximally along the length of the sleeve. The device can be a cutter or an enlarged diameter bursting element that moves through the lumen of the stent to rupture the sleeve progressively.
EP-A-1679095 proposes a PTFE material, longitudinally drawn, for a sheath over a stent that itself overlies a PET balloon of a balloon catheter delivery vehicle for the stent. Inflation of the balloon ruptures the sheath. The ruptured sheath is pulled from its location between the stented bodily tissue and the abluminal surface of the stent when the catheter is pulled proximally away from the site of stenting and the stent placed there.